A conventional cellular telephone may be configured to operate according to a number of different transmission standards such as, for example, the Global System for Mobile Telecommunications (GSM) standard, or the Universal Mobile Telecommunications System (UMTS) standard.
A cellular telephone typically includes a filter within its signal transmission and/or receive channels such as, for example, an anti-aliasing filter or a channel selection filter (of the low-pass type) designed to a given standard. The filter is typically chosen from a set of filters having different topologies and/or orders embedded within the transmission and/or receive channels.
Certain criteria such as, for example, the passband width or the ripple, are variable depending on the type of transmission standard desired. Adapted topologies and/or filter orders allow the required performance to be attained. Consequently, depending on the transmission standard detected by the cellular phone or chosen by the user, one of the filters is connected to the transmission and/or receive channel for optimal filtering.
Conventionally, filters constructed from transconductance amplifiers are adapted to form the various aforementioned filters and, in particular, the Butterworth, Chebychev or elliptical type filters. For each cellular telephone, all filters required for the various standards had to be considered and selected according to the communications standard detected.
There is therefore a need for a filtering device with flexible architecture, and in particular, a filtering device from which using the same initial structure, the device can selectively present a different topology and/or an order.